Although Long-term group psychotherapy is an often recommended form of treatment for patients with personality disorders (PDs) and an extensive clinical literature exists to endorse such treatment, empirical support is lacking. We know little about how such groups affect patients with PDs and methods to measure therapeutic changes specific to this population are lacking. In this project we will examine the process of change for patients with one of three different PDs (avoidant, obsessive-compulsive, borderline) in 18-month, time-limited, interpersonal-interactional group psychotherapy. Subjects for this study will be 100 patients, the majority of whom have one of these three PDs. Approximately 12 psychotherapy groups will be run according to a standardized approach to the long-term group treatment of PDs. This study will measure outcome for this population from a variety of important perspectives, including novel ones, such as the patients' changes as they are manifested in their within-group behaviors and group members' ratings of one another's outcomes. Aside from investigating the very important issue of outcome in PD patients, this investigation also opens up a number of other significant areas relevant to the understanding and treatment of those with personality pathology.